Wellhead equipment utilized in connection with an oil or gas wellbore may be subject to extreme conditions during oilfield operations, such as, for example, cementing, acidizing, fracturing, and/or gravel packing of a subterranean wellbore. Wellhead isolation tools are often used to protect wellhead equipment from excessive pressures, temperatures, and flow rates encountered during such oilfield operations. An exemplary wellhead isolation tool is adapted to position and secure a mandrel within a wellhead. The mandrel includes a packoff assembly, which is adapted to isolate the wellhead equipment from fluid flowing through the mandrel to and from the oil or gas wellbore. However, in the field, the performance and reliability of the mandrel and packoff assembly are often an issue because of the extreme duty cycles experienced by wellhead isolation tools during oilfield operations. For example, during oil or gas wellbore fracturing operations, wellhead equipment may be subject to a fluid or slurry pressure of up to 20,000 psi or more. As a result, the high pressures and flow rates encountered during oil or gas wellbore fracturing operations often cause packoff assemblies to “lift-off” from a sealing surface, allowing the fracturing fluid or slurry to leak or blow by the packoff assembly and into the wellhead equipment. Moreover, in order to protect the packoff assembly from damage, it is important to provide support against external forces applied to the mandrel along the longitudinal axis thereof, in both axial directions. Therefore, what is needed is an apparatus, system, or method that addresses one or more of the foregoing issues, among one or more other issues.